1. Field of the Invention
This invention relates to improvements in an internal combustion engine of the split type operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
It is known and desirable to increase the efficiency of a multicylinder internal combustion engine by reducing the number of cylinders on which the engine operates under predetermined engine operating conditions, particularly conditions of low engine load. Control systems have already been proposed which disable a number of cylinders in a multicylinder internal combustion engine by suppressing the supply of fuel to certain cylinders or by preventing the operation of the intake and exhaust valves of selected cylinders. Under given load conditions, the disablement of some of the cylinders of the engine increases the load on those remaining in operation and, as a result, the energy conversion efficiency is increased.
It is common practice to introduce exhaust gases into the disabled cylinders through an EGR valve adapted to open under given low load conditions and to prevent the introduced exhaust gases from flowing to the cylinders remaining in operation by the use of a stop valve adapted to close in timed relation with the opening of the EGR valve. This is effective to suppress pumping loss in the disabled cylinders and attain higher fuel economy.
With such conventional split type internal combustion engines, one difficulty has been assuring that the EGR and stop valves were operated at the proper timing. If any trouble occurs to open the EGR and stop valves simultaneously, a great amount exhaust gases will flow over the stop valve, causing many problems.
The present invention provides an improved split type internal combustion engine wherein means is provided for preventing the simultaneous opening of the stop and EGR valves.